Embodiments of the invention relate generally to improving the structure of a bipolar transistor (also known as a bipolar junction transistor or “BJT”) for high frequency applications (i.e., above approximately five hundred gigahertz (GHz)). More specifically, embodiments of the invention include the structure of a bipolar transistor and methods of forming the disclosed structure.
In integrated circuit (IC) structures, a transistor is a critical component for implementing proposed circuitry designs. In analog circuitry, numerous functions can be implemented with bipolar transistors. For example, the ability to control the flow of electric current between terminals of the transistor can allow the transistor to act as a switch, and therefore act as a building block for logic functions. Generally, a bipolar transistor includes three electrical terminals: a collector, a base, and an emitter. The flow of electricity between the collector and emitter terminals of a bipolar transistor can be controlled by adjusting the electric current or voltage difference between the base and emitter terminals.
In circuitry configured to operate at frequencies higher than approximately three hundred GHz, bipolar transistors may offer more reliable performance than other types of transistors, e.g., metal oxide semiconductor field effect transistors (MOSFETs). Bipolar transistors can be manufactured with equipment and techniques suitable for creating other microelectronic devices. The effectiveness of a bipolar transistor depends in part on parasitic losses (e.g., resistances and capacitances) within components of the transistor structure being used. As a result, the physical structure of a bipolar transistor can influence the reliability and performance of the transistor when it is implemented in a product or larger system.